Electrical resistor units



' Filed Aug. 27, 1952 Feb. 17, 1959 Q W, KUHN ETAL 2,874,257

EILJEICTRICAL.v RESISTOR UNITS 2 Sheets-Sheet yl 3o FIGLI f "valli". Y

INVENTORS N 44 CLARENCE w KUHN GUY E, @A

F716. 5 By Feb. 17, 1959 C, wl KUHN ErAL 2,874,257

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INVENToRs CZAEE/VCE l/V. KUHN GU Y l?, RADLEY BY -A/T HEY lllnited States Patent O "ice ELECTRICAL 'RESIS'IOR UNITS Application August 27, 1952, Serial No. 306,574

6 Claims. (Cl. 201-74) This invention relates to improvements in resistors,

particularly the type used in the dynamic braking of electric motors.

Resistors of this type are described and claimed the Kuhn and Welch Patent No. 2,680,178, granted June 1, 1954, for Resistor Unit and Method of Making the Same, and assigned to the same assignee as the present application. The capacity of such units is limited, however, by overheating occurring in the loops or reflexes of the grid and in the insulators where such loops are supported.

It is the object of this invention therefore to provide a resistor in which overheating in the loops of the grid and the insulator where such loops are supported is prevented and the capacity of the resistor increased without appreciable increase in physical dimensions.

This object is obtained by supporting the grid by brackets which hold the loops'away from the insulators and in the cooling air stream so that heat will be dissipated from the loops as readily as from the lengths between the loops and hence prevent any damaging overheated areas in such loops or insulators.

' The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, to gether with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings in which:

Figure 1 is a horizontal plane sectional view of a lirst form of resistor embodying the present invention;

Fig. 2 is an enlarged fragmentary sectional view taken on the line 2 2 of Fig. 1;

Fig. 3 is a sectional view taken on the line 3--3 of Fig. 2;

Fig. 4 is an enlarged sectional view similar to Fig. 3 of a second form of resistor embodying the present invention;

Fig. 5 is an enlarged sectional view similar to Fig. 2 of a third form of resistor embodying the present invention;

Fig. 6 is a sectional view taken on the line 6- 6 of Fig. 5;

Fig. 7 is a fragmentary horizontal plane sectional view of a fourth form of resistor embodying the present invention;

Fig. 8 is an enlarged fragmentary sectional view taken on the line 8-8 of Fig. 7;

Fig. 9 is a fragmentary horizontal plane sectional view of a fifthform of resistor embodying the present invention;

Fig. 10 is an enlarged fragmentary sectional view taken on the line 10-10 of Fig. 9;

Fig; 11 is an enlarged fragmentary sectional view taken 'on the line 11-11 of Fig. 8;

Fig. 12 is an enlarged fragmentary sectional view taken on the line 12--12 of Fig. 8;

2,874,257 Patented Feb. 17, 1959 Fig. 13 is an enlarged fragmentary sectional view taken on the line 13--13 of Fig. 8;

Fig. 14 is an enlarged fragmentary sectional view taken on the line 14-14 of Fig. 8;

Fig. 15 is an enlarged fragmentary sectional view taken on the line 15-15 of Fig. 8;

Fig. 16 is an enlarged fragmentary sectional view taken on the line 16-16 of Fig. 10, part being broken away for clarity;

Fig. 17 is an enlarged fragmentary sectional view taken on the line 17-17 of Fig. 10; and

Fig. 18 is an enlarged fragmentary sectional view similar to Fig. 17 of a sixth form of resistor embodying the present invention.

In all of the forms of the resistor shown and described the metal frame has side channels 10 and 12, end plates 14 and 16, pressure plate 32 and compression springs 30 all identical in structure and function with the frame disclosed in the aforementioned Patent No. 2,680,178. The grid 44 is of the same construction as that described and claimed in said Patent No. 2,680,178. In 4the first three forms (Figs. 1 to 6, inclusive) the insulators 34 are the same as those of said Patent No. 2,680,178 and have spaced grooves 36 adapted to hold the brackets of the grid 44. As in said patent a sheet of mica 40 or other like insulating material is placed between the metal frame and the insulators.

In order to prevent overheating of the loops or reflexes 46 and of the insulators, the loops 46 are supported by metal clips, brackets or hangers extending between the insulators and loops. These brackets are long enough to keep the loops 46 out of heat conducting contact with the insulators and to place such loops in the same cooling air stream as the lengths 48. This avoids the heat insulation of the loops by the insulator and enables the loops to lose heat as rapidly as the remainder of the grid. It also prevents direct transfer of heat from the highly heated loops to the insulators at the place of support. Such heat as is transferred to the insulators is the result of direct radiation from the loop and by conduction through such brackets. The heat so transfer-red is not, however, sufficient to injure the insulation.

In the first, second and third forms aforementioned the insulators 34 and grooves 36 are of the same design as those of said Patent No. 2,680,178. However, the use of brackets lessens the eiective length of the lengths 48 and in some applications it may be necessary to slightly lengthen the end plates 14 and 16 to produce a comparable resistance.

In the first form (Figs. 1, 2 and 3) a bracket 51 conn sisting of a U-shaped metal piece has legs straddling and spot welded to the loop 46 and a bridge portion seated in the groove 36. Substantially no current is carried by the bracket 51 and hence the only heat generated therein is that caused by conduction from the loop 46. Hence the insulator 34 will not be excessively heated and the loop 46 being held out away from the insulator in the cooling air stream for the grid 44 will not get hotter than the lengths 48.

The second form (Fig. 4) is the same as the irst form except that the bracket 51 is secured by rivets 53 to the sides of the loop 46. This eliminates the spot welding and the attendant heat treatment and also decreases the conduction of heat from the grid to the bracket.

The bracket 55 of the third form (Figs. S and 6) consists of a strip of metal having only one leg spot welded or riveted to one side of the loop 46. Such strip is olset as shown so that its outer end is substantially in alinement with the center of the loop 46. With such outer end positionedin a groove 36 the loop .46 will be positioned in proper alinement with such groove and the loop 46 will be held in the same cooling air stream as the rc- 

